The present invention relates to an improved low pressure microwave drying apparatus, more particularly to a low pressure microwave drying apparatus free from the occurrence of the glow discharge phenomenon.
The low pressure microwave drying apparatus is known as a means for drying a substance by irradiating it with microwaves under conditions which restrict the rise of the temperature therein. However, in the case where a substance is dried by the conventional low pressure microwave drying apparatus, the glow discharge may occur during the irradiation of microwaves, depending on the degree of pressure reduction. If glow discharge occurs during the drying procedure, this causes various disadvantages, among which can be mentioned detrimental effects on the substance to be dried such as chemical change of its constituents and partial overheating, harmful effects on the drying apparatus itself such as damage to the magnetron, and loss of microwave energy.